Noun. Pronounced: "chum'-buh-loan"
1) term originally used primarily in and around the Chicago area to describe a person who is easily tricked into doing something directly counter to their own personal self-interest; 2) since the 2008 presidential election, also applied to anyone outside the Chicago area who exhibits similar incapacity for sound judgment; 3) a person so devoid of common sense that they can be manipulated in any number of ways without having the slightest clue as to how ignorant and/or stupid they are.
Application: Originally applied to lesser-educated Caucasians of lower intelligence who tend to believe anything that government officials and the news media tell them; since the 2008 election, now also applied to better-educated and intelligent Caucasians of all ages and genders who are totally devoid of any street smarts whatsoever, as well as to members of all other races, age groups and genders who also continue to believe whatever is told to them by government and media representatives evidence to the contrary notwithstanding.

idiot, stupid - Popularized by Chicago newspaper columnist John Kass after first hearing the word spoken in testimony by mob messenger boy Anthony "Twan" Doyle during a 2007 federal trial. While working for the mob, Doyle got himself hired into the Chicago Police Department evidence department in order to remove or destroy DNA and other evidence of mob homicides.

Actual example: "I gave him lip service," Doyle said. "I didn't know what he was talking about. I don't wanna look like a chumbolone, an idiot, stupid," Doyle said from the witness stand.